8 10 MAN 



great nucleus of the brain stem has manifested the progressive modifica- 

 tions seen in the intermechate primates. At length in the great anthropoids 

 it begins to disclose that outhne familiar both in conliguration and dciinitioti 

 which finally is expressed in the richly convoluted nucleus of the human 

 brain. Assuming the correctness of the interpretation already ascribed to 

 the inferior olivary nucleus in its relation to the simultaneous movements 

 of the head, eye and hand as well as the facilitating of all skilled move- 

 ments, it will be clear that a functional expression of this expansion in the 

 primate order has kept pace with the structural e\olution ol the nucleus. 

 For example, the skilled performances of man in w liich sinuiltaneous move- 

 ments of the eyeball, the hand and the head are essential, as compared with 

 those of the lemur or marmoset, appear to be greatly in advance of such 

 acts in these lower prnnates. 



The bod\ of the central gra\' matter has completed its dorsal migration 

 and lies in a position forming the floor of the f )urth \entricle. In its \entro- 

 mesial portion is the clearly dillerentiated hypoglossal nucleus (Nhy), 

 separated from which b\- the funiculus separans is the dorsal vagal nucleus 

 (N vd). The emergent fibers from the twelfth nerve (N i 2) make their way 

 forward from the nucleus toward the inferior olivary body, while the entering 

 libers of the vagus nerve pass through the lateral aspect of the periphery 

 and make tluMr way to the dorsal sensory luieleus. They traverse in so doing 

 the restiform body, the descending trigeminal faseieulus and the sub- 

 stantia gelatinosa of Rolando (NR). Ventrolateral to the dorsal vagal 

 nucleus is a colkx'tion of densel\' m\elini/A'd libers surrounded by a nuclear 

 mass. This comprises the nueU'us solitarlns ( N f s ) and its accompan\ing 

 fasciculus solitarius. In the most lateral position in the dorsal held is 

 the cephalic extremity of the nueh'us of BlunuMUiu (NBH surrounded by 

 a few myelinated libers arising in the column of Bnrdaeh. l-'eri[)heral to 

 this is the dense myelinized bundle constituting the restiform body (.hie) 



